The present invention concerns a two-colour liquid crystal display assembly allowing a high contrast and purity of colour to be obtained by a particular arrangement of the different elements forming the display assembly.
The invention allows the information provided by any type of electronic apparatus to be made easier to read and more attractive, in particular the time-related and non-time-related information provided by a timepiece.
With reference for example to the chapter by T. J. Scheffer entitled xe2x80x9cLiquid crystal color displayxe2x80x9d in the work on xe2x80x9cNon emissive Electrooptic Displayxe2x80x9d (1976, editors A. R. Kmetz and F. K. von Willisen), arrangements allowing information to be displayed in a first colour on a background of a second colour are known. In order to be easy to read, it is desirable to have a high contrast, which can ideally be obtained when the first and second colours are complementary colours such as green and red or yellow and blue.
In the known constructions of the prior art, the display assembly basically includes, starting from the side of the observer or viewer, an information display module, on either side of which are arranged two linear polarisers at least one of which is selective of the first colour, a coloured filter corresponding to the second colour and a metal reflector at the back. As will be explained in more detail hereinafter, such an arrangement prevents the first and second colours from being perfectly independent, so that there will be for example a yellow display on a green background using a blue selective polariser and a yellow filter.
Conversely, still within the hypothesis of one or several blue selective polarisers and a yellow filter, the present invention enables a yellow display to be obtained on a brilliant blue background.
The invention therefore concerns a two-colour display assembly including a first device determining a first colour and a second device determining a second colour. The first device is formed of a liquid crystal display module, the switching configurations of which are determined by an electronic control unit powered by an energy source, said display module including two linear polarisers disposed at the front and the back of said module and at least one of which is selective of a first colour. The second device includes a coloured filter determining the second colour. The display assembly is characterised in that the axes of polarisation of the polarisers of the first device are parallel to each other, in that the coloured filter of the second device includes at the front a reflective polariser whose axis of polarisation is parallel to the axes of polarisation of the two polarisers of the first device, and at the back a reflective element and in that the control unit enables a switching configuration to be defined displaying an item of information in the first colour on a background corresponding to the second colour or vice versa.
As will be shown in the detailed description, this precise arrangement of all the constituent elements of the display assembly according to the invention, enables the first and second colours to be independent with very high efficiency, i.e. a high colour purity to be obtained, which contributes to increasing the contrast and thus allows, in particular, the displayed information to be read more easily.
The reflective element of the second display may be a metal reflector which will reflect all of the incident light, a transflective reflector which will only partially reflect or a reflective polariser crossed with the reflective front polariser which will allow part of the incident light to pass. In this latter case, the light going beyond the reflective element will allow a second display placed at the back of the second device to be made visible. Conversely, in these two latter cases, it will be possible to place a light source (diode, electroluminescent sheet, etc.) at the back of the second device, which will increase the luminosity of the display, for example in night vision.
As will be seen hereinafter, the two polarisers of the first display can both be polarisers selective of the first colour.
The liquid crystal display module may be formed by a single matrix display cell or a liquid crystal segment cell. This display module can also have a more complex structure, for example formed by an optical valve and by a matrix or segment cell to allow contrast inversion, as will be shown in the following examples.